1. Technical Field
The present invention relates to an actuator device that includes a piezoelectric element, a liquid-jet head and a liquid-jet apparatus, the liquid-jet head and the liquid-jet apparatus including an actuator device as a driver for spraying liquid droplets.
2. Related Art
An actuator device that includes a piezoelectric element which is displaced according to an applied voltage is mounted on a liquid-jet head that sprays liquid droplets. The liquid-jet apparatus that includes the liquid-jet head may be an ink-jet recording apparatus with an ink-jet recording head having a plurality of pressure generating chambers that generates pressure for ejecting ink droplets by using the piezoelectric element or a heating element, a common reservoir that supplies ink to each pressure generating chamber, and a nozzle orifice communicating with each pressure generating chamber. In the ink-jet recording apparatus, an ejecting energy is applied to the ink in the pressure generating chamber that communicates with a nozzle corresponding to a printing signal, thereby ejecting ink droplets from the nozzle orifice.
As described above, the ink-jet recording head can be classified into two types. In one of the two types of the ink-jet recording head, the heating element such as a resistance line in which Joule heat is generated according to a drive signal is located in the pressure generating chamber, and ink droplets are ejected from the nozzle orifice by using bubbles that are generated by the heating element. In the other (referred to as a piezoelectric vibration type) of the two types of the ink-jet recording head, a part of the pressure generating chamber is configured by using a vibration plate, and ink droplets are ejected from the nozzle orifice by deforming the vibration plate by using the piezoelectric element.
A piezoelectric vibration type ink-jet recording head that employs a piezoelectric actuator which has an axial vibration mode in which the piezoelectric element elongates and shrinks in an axial direction and a piezoelectric vibration type ink-jet recording head that employs a piezoelectric actuator which has a flexural vibration mode have been put to practical use.
In the former piezoelectric vibration type ink-jet recording head, a volume of the pressure generating chamber is changed by contacting an edge face of the piezoelectric element with the vibration plate, thereby producing a head suitable for high density printing. However, a difficult process in which the piezoelectric element is carved for a pectinate shape so that the piezoelectric element is matched to an arrangement pitch of the nozzle orifice or a process in which the carved piezoelectric element is positioned and fixed to the pressure generating chamber is needed, thereby complicating manufacturing processes.
In the latter piezoelectric vibration type ink-jet recording head, the piezoelectric element can be built in the vibration plate by a relatively simple process such as attaching a green sheet made of a piezoelectric material in accordance with a shape of the pressure generating chamber and calcining them. However, since the flexural vibration is used, some area is needed. Accordingly, a high density arrangement is difficult.
In order to solve a problem of the latter recording head, it is disclosed that a uniform piezoelectric material layer is formed on the entire surface of the vibration plate by using a film formation technique, and each piezoelectric element is independently formed in each pressure generating chamber by carving the piezoelectric material layer in accordance with the shape corresponding to the pressure generating chamber by lithography (refer to JP-A-5-286131).
Accordingly, a process of attaching the piezoelectric element to the vibration plate is not needed, and the piezoelectric element is densely built in by lithography which is a precise and simple method. Furthermore, the thickness of the piezoelectric element is reduced, thereby enabling high speed drive.
Strain of the piezoelectric element is maximized in an engineered domain structure in which an angle of θ between the polarization axis (dipole) and an electric field direction is the same at any other domain of the piezoelectric element. In a rhombohedral system, when electric field E is applied in crystalline orientation (001), the maximum strain of the piezoelectric element can be obtained. Composition of piezoelectric crystal is improved so that a piezoelectric constant d31 or d33 that denotes easiness of strain of piezoelectric substance can be large. Lead magnesium niobate-lead titanate (PMN-PT) (refer to JP-T-2001-509312) or lead zinc niobate-lead titanate (PZN-PT) is known as relaxor ferroelectric single-crystal.
However, although the piezoelectric constant d33 of the aforementioned ferroelectric substance is no less than 2500 pC/N, when a load is applied to the ferroelectric substance, the maximum generated stress is about 20 MPa. On the contrary, it has been found that the stress of lead zirconate titanate (PZT) is 35 Mpa, which is greater than that of the aforementioned ferroelectric substance.